Polyfet LR401

Hello
anybody using this device or similer from polyfet
we are facing some problem with LR401 . The device was biased in this manner.
Input was terminated through an circulator and output was terminated with a 40 dB pad and then connected to a spectrum analyser. Input and output matching network was also provided . First drain supply 28 V was given and then gate voltage was gradually increased from 1V . Idq incresed gradually to .04A upon increase of Vgg then a sudden jump in Idq was noticed ( upto .11 A).
there was no oscillation seen on spectrum analyser and the device was found to be damaged.
there after no more current was drawn and gate voltage was constant, even though gate drive was increased. gate resistance was found to be a few hundread ohms.

We lost three devices. Please help

thanks in advance

Hi,

I've had quite a bit of experience with mosfets; is this the DMOS or LDMOS? If the latter, then there's probably a parasitic bipolar transistor intrisic to the device and you may have missed the oscillation on the SA. If you have a curve tracer you can determine if this is the case by looking at it's output characteristics. I've noticed that most LDMOS devices have the PBT, it's just a matter of what degree/sensitivity and whether the external circuitry is sympathetic and enhances it.

Regards,
MoonShine